In semiconductor fabrication, various layers of insulating material, semiconducting material and conducting material are formed to produce a semiconductor device. The layers are patterned to create features that taken together, form elements such as transistors, capacitors, and resistors. These elements are then interconnected to achieve a desired electrical function, thereby producing an integrated circuit (IC) device. In a conventional process, the resistors are formed by doping or implanting doping ions with a relatively small doping concentration into a substrate. The doping concentration often varies according to different resistances of the resistors. Therefore, the resistors with different resistances have to be formed respectively by the aforementioned doping or implanting processes using different doping concentrations. Further, the operation of forming the resistors cannot be performed by combining with other processes. For example, a source/drain (or a gate) may be formed using an implanting process. However, a doping concentration of the doping ions used to form the source/drain (or the gate) is greater than that used to form the resistors due to consideration of the source/drain (or the gate) with a relatively high conductivity. Thus, the process of fabricating the semiconductor device with resistors is complicated and has high fabrication cost.